Stripper-plate alignment system and die set

ABSTRACT

A stripper-plate for a progressive die sets is provided including open-ended tubular guide bushings that project outwardly from at least one side. A first anti-friction bearing assembly is positioned within each of the guide bushings, and a second anti-friction bearing assembly is positioned on an outer surface of each of the guide bushings. A die set is also provided including an upper die shoe having a plurality of guide posts arranged in a pattern and projecting outwardly from a surface. A lower die shoe is arranged in confronting relation to the surface of the upper die shoe, and includes a first plurality of open ended tubular guide bushings positioned so as to each receive a corresponding one of the guide posts. A first anti-friction bearing assembly is positioned within each of the guide bushings. A stripper-plate is positioned between the upper die shoe and the lower die shoes, and includes a second plurality of open-ended tubular guide bushings each having an outer surface and an inner surface. The second guide bushings project outwardly toward the lower die shoe in a pattern that corresponds to the pattern of guide posts. Each of the first anti-friction bearing assemblies slidingly engages an outer surface of a corresponding one of the second guide bushing. Each of the second guide bushings includes a second anti-friction bearing assembly that is positioned on an inner surface so as to engage a corresponding one of the guide posts.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional PatentApplication No. 60/398,855, filed Jul. 26, 2002.

FIELD OF THE INVENTION

[0002] The present invention generally relates to metal formingequipment and, more particularly, to progressive metal stamping dies.

BACKGROUND OF THE INVENTION

[0003] Progressive metal stamping in which a metal strip or the like isguided along a predetermined path through a die set in cadence with theoperation of a reciprocating press is well known. Prior art metalstamping die sets typically consist of confronting upper and lower dieshoes, where one or the other of the die shoes includes two or moresolid metal guide posts (usually four) affixed to it, and the other ofthe die shoes includes a corresponding number of bushings affixed to it.The bushings receive the guide posts, and thereby serve to guide theshoes as they are brought together during reciprocating press operationfor the forming or punching of a metal strip. A plurality of tools arepositioned on the inner punching of a metal strip. A plurality of toolsare positioned on the inner confronting surfaces of the upper and lowerdie shoes that are circumscribed by the posts and bushings. These toolsare shaped and sized to enable piercing, punching, drawing, or otheroperations to be performed upon the metal strip as it progresses throughthe die set.

[0004] Upon each reciprocating movement or “stroke”of the press, themetal strip is lifted and then advanced by one step through the die set.The tools that are located on the upper die shoe, above the metal strip,thus move toward and away from the surface of the metal strip duringeach full cycle of the press. These tools, often simply referred to as“punches,” are guided through a stripper-plate which is located justabove the metal strip. The stripper-plate often has a plurality of guideopenings to guide the punches toward the metal strip, and to retain themetal strip in position during the punching, piercing, or drawingoperation, while permitting movement of the metal strip as it isprogressively fed through the die between punching strokes. Thestripper-plate is pressed by releasable spring pressure against themetal strip during each downward stroke of the press. The punches passthrough the guide openings in the stripper-plate during the downwardstroke of the press and toward the metal strip. The punches engage orpenetrate the metal strip and then are retracted with the upward strokeof the press. During the upward stroke of the press, as the punches arepulled away from the metal strip, the metal strip is pulled or“stripped” off the punches by the stripper-plate. At the same time, thespring pressure is,released from the stripper-plate, which then alsomoves away from the metal strip, thereby releasing the metal strip sothat it may be advanced an incremental step through the die set prior tothe next downward stroke.

[0005] Because of the complex timed movement of the foregoing elements,it is essential that accuracy be maintained in guiding the upper andlower die shoes together, so that the mating parts of the die set, i.e.,tools and recesses, cooperate as intended, otherwise damage anddestruction of the tools mounted on the die set, and possibly also thepress, itself, may result. Thus, the solid guide post and bushing systemalong with the stripper-plate are essential to optimum progressive dieand press operations.

[0006] In order to make this metal forming system more rigid and therebyafford greater accuracy, single ball bearing cages located between theouter surface of the guide posts and guide bushings have been used inmany prior art progressive dies. As alignment of the punching componentshas become more critical over time, the stripper-plate has become themechanism to guide the male punching components into the femalecomponents. To accomplish this critical task, a second system of guideposts and bushings has often been added to the first set of guide postsand bushings. The second system of guide posts and bushings are locatedon the interior confronting surfaces of the die shoes. As a function ofavailable space within the die set and press, this second system ofguide posts necessarily has to be smaller than the first guide posts andbushings that guide the upper and lower die shoes together. As aconsequence, prior art die sets have increased accuracy through greaterrigidity in the system by trading a smaller bearing surface to guide thestripper-plate and therethrough guide the punches, and a greater bearingsurface to guide the upper die shoe. Unfortunately, the upper die shoeoften does not require the same accuracy as the stripper-plate. Thesecond system of guide posts and bushings also limits the effective worksurface available in the die set for the varied operations now requiredfrom high speed metal stamping.

[0007] One way to increase both the bearing surface and guidance of thestripper-plate is to use very large (diameter) guide posts and guidethem directly into bushings in the lower shoe. This technique has beenfound, however, to add considerable weight to the stripper-plate,requiring larger spring constant springs to provide additionalreleasable spring pressure in an already crowded workspace. Thistechnique also often inhibits press running speeds.

[0008] As a consequence, there has been a long felt need for a metalstamping die set that has a maximum workspace available between theupper and lower die shoes, while at the same time, provides forreliable, high speed press operation and greater die set andstripper-plate accuracy.

SUMMARY OF THE INVENTION

[0009] The present invention provides a metal stamping system includinga press having a reciprocating ram. A bulbous protrusion projectsoutwardly from an end of the ram. An upper die shoe is providedincluding (i) a recess formed in a top surface, the recess beingcomplementary to the bulbous protrusion, and (ii) a plurality of guideposts arranged in a pattern and projecting outwardly from a bottomsurface. During operation of the system, the bulbous protrusion isfreely received within the complementary recess, i.e., the bulbousprotrusion is not fastened to the upper shoe. A lower die shoe ispositioned in confronting relation to the surface and includes a firstplurality of open ended tubular guide bushings each having a firstanti-friction bearing assembly positioned within a central passageway,and each located so as to receive a corresponding one of the guideposts. A stripper-plate is positioned between the upper die shoe and thelower die shoe. The stripper-plate includes a second plurality ofopen-ended tubular guide bushings each having an outer surface and aninner surface and each projecting outwardly toward the lower die shoe ina pattern corresponding to the pattern of guide posts. In this way, eachof the first anti-friction bearing assemblies slidingly engages an outersurface of a corresponding one of the second open ended guide bushing.Each of the second plurality of open-ended guide bushings includes asecond anti-friction bearing assembly that is positioned on the innersurface so as to engage a corresponding one of the guide posts. Springmeans are provided for separating the upper shoe from the lower shoeafter each downward stroke of the ram.

[0010] In an alternative embodiment of the invention, a die set isprovided of the type that is to be reciprocatingly driven in a stampingpress. The die set of the invention includes an upper die shoe including(i) a recess formed in a top surface, the recess being complementary toa bulbous protrusion located on a ram portion of the press, and (ii) aplurality of guide posts arranged in a pattern and projecting outwardlyfrom a bottom surface. The bulbous protrusion is freely received withinthe complementary recess. A lower die shoe is positioned in confrontingrelation to the surface, and includes a first plurality of open endedtubular guide bushings each having a first anti-friction bearingassembly positioned within a central passageway, and each located so asto receive a corresponding one of the guide posts. A stripper-plate ispositioned between the upper die shoe and the lower die shoe. Thestripper-plate includes a second plurality of open-ended tubular guidebushings, each having an outer surface and an inner surface and eachprojecting outwardly toward the lower die shoe in a patterncorresponding to the pattern of guide posts. In this way, each of thefirst anti-friction bearing assemblies slidingly engages an outersurface of a corresponding one of the second open ended guide bushing.Each of the second plurality of open-ended guide bushings includes asecond anti-friction bearing assembly positioned on the inner surface soas to engage a corresponding one of the guide posts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] These and other features and advantages of the present inventionwill be more fully disclosed in, or rendered obvious by, the followingdetailed description of the preferred embodiments of the invention,which are to be considered together with the accompanying drawings,wherein like numbers refer to like parts and further wherein:

[0012]FIG. 1 is a partially broken-away, front elevational view of ahigh speed metal stamping press including a die set and stripperalignment system formed in accordance with the present invention;

[0013]FIG. 2 is a top elevational view of an upper die shoe;

[0014]FIG. 3 is a side elevational view of the upper die shoe shown inFIG. 2;

[0015]FIG. 4 is a top elevational view of a lower die shoe;

[0016]FIG. 5 is a side view of the lower die shoe shown in FIG. 4;

[0017]FIG. 6 is a top view of a stripper-plate formed in accordance withthe present invention;

[0018]FIG. 7 is a side view of the stripper-plate shown in FIG. 6;

[0019]FIG. 8 is a partially broken-away, cross-sectional view ofassembled upper and lower die shoes, a stripper-plate, and including astripper-plate alignment system formed in accordance with the presentinvention;

[0020]FIG. 9 is a partially broken-away, partially phantom, view of aportion of the stamping press shown in FIG. 1, having a side-by-sidepair of die sets, each including a stripper-plate alignment systemformed in accordance with the invention, mounted to an intermediatelocator plate positioned on the bolster of the press;

[0021]FIG. 10 is a side elevational view, partially in phantom, of apair of upper die shoes arranged in accordance with an alternativeembodiment of the invention;

[0022]FIG. 11 is a side elevational view, partially in phantom, of apair of stripper-plates arranged in accordance with an alternativeembodiment of the invention; and

[0023]FIG. 12 is a side elevational view, partially in phantom, of asingle lower die shoe arranged in accordance with an alternativeembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] This description of preferred embodiments is intended to be readin connection with the accompanying drawings, which are to be consideredpart of the entire written description of this invention. The drawingfigures are not necessarily to scale and certain features of theinvention may be shown exaggerated in scale or in somewhat schematicform in the interest of clarity and conciseness. In the description,relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and“bottom” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing figure underdiscussion. These relative terms are for convenience of description andnormally are not intended to require a particular orientation. Termsincluding “inwardly” versus “outwardly,” “longitudinal” versus “lateral”and the like are to be interpreted relative to one another or relativeto an axis of elongation, or an axis or center of rotation, asappropriate. Terms concerning attachments, coupling and the like, suchas “connected” and “interconnected,” refer to a relationship whereinstructures are secured or attached to one another either directly orindirectly through intervening structures, as well as both movable orrigid attachments or relationships, unless expressly describedotherwise. The term “operatively connected” is such an attachment,coupling or connection that allows the pertinent structures to operateas intended by virtue of that relationship. In the claims,means-plus-function clauses are intended to cover the structuresdescribed, suggested, or rendered obvious by the written description ordrawings for performing the recited function, including not onlystructural equivalents but also equivalent structures.

[0025] Referring to FIG. 1, a die set 2 comprising a stripper-platealignment system 5 formed in accordance with the present invention isoften mounted within a high speed stamping and forming press 8 of thetype well known in the art. For example, a typical high speed stampingand forming press 8 includes a ram 11 that moves toward and away from abolster plate 12 at a rate of between approximately 1,000-3000 strokesper minute, or more. The length of the stroke is often about 0.25inches. An electric motor 15 is coupled to a drive shaft 18 having aneccentric 19 which drives ram 11 by means of a crank 20. Drive shaft 18and crank 20 are journaled in hydrostatic bearings, and ram 11 isjournaled in a linear hydrostatic bearing, including fluid conduits, allof which are specially designed to allow high speed stamping and formingpress 8 to operate at the above-mentioned 1,000-3000 strokes per minute.In the present invention, end 21 of ram 11 includes an outwardlyprojecting bulbous protrusion 22, such as a chord of a sphere, on thesurface of ram 11 that opposes bolster plate 12. In some arrangements,an intermediary plate 23, having an outwardly projecting bulbousprotrusion 22, may be positioned between upper die shoe 25 and end 21 ofram 11 so as to distribute forces more equally, and allow forretrofitting of prior art presses in the field (FIGS. 9 and 10).

[0026] Referring to FIGS. 1-5, die set 2 comprises an upper shoe 26attached to and carried by ram 11, and a mating lower die shoe 26secured to bolster plate 12 in a conventional manner well known in theart. Two or more guide posts 30 project downwardly from upper die shoe25, and are received within internal passageways 32 of correspondinglypositioned guide bushings 31 mounted in lower die shoe 26. In onepreferred embodiment of the present invention, six mating pairs of guideposts 30 and guide bushings 31 are arranged on upper die shoe 25 andlower die shoe 26. Each guide post 30 includes a recess 33 defined at afree end 34 (FIG. 8). Upper die shoe 25 also includes a ram couplercomprising a recess 24 defined in a top surface. Ram coupler 24 isadapted to non-fixedly engage complementarily shaped bulbous protrusion22 on the end of ram 11. The engagement is such that ram 11 can forceupper die shoe 25 downwardly toward lower die shoe 26. Some relativemotion is permitted within the coupling between ram 11 and upper dieshoe 25 as a result of the implementation of stripper-plate alignmentsystem 5.

[0027] Referring to FIGS. 1, 6-7, and 8, a stripper-plate 35 is locatedbetween upper die shoe 25 and lower die shoe 26, and is maintained inposition via stripper-plate alignment system 5 (FIGS. 1 and 8).Stripper-plate 35 comprises one or more central openings 36 that receivepunches and the like (not shown) and peripheral through-bores 37arranged in a pattern that corresponds to the pattern of guide posts 30and guide bushings 31 on upper die shoe 25 and lower die shoe 26.

[0028] Referring to FIGS. 6-8; stripper-plate alignment system 5 isassembled between upper shoe 25 and lower shoe 26, and comprises aplurality of stripper guide bushings 40, a plurality of internalanti-friction bearing assemblies 42, a plurality of externalanti-friction bearing assemblies 44, and a plurality of return springs46. In a preferred embodiment of the invention, there is at least onestripper guide bushing 40, one internal and one external anti-frictionbearing assemblies 42,44, and a return spring 46 associated with eachpair of guide posts 30 and guide bushings 31. Of course, otherarrangements of return springs are possible, as long as such structuresallow for the axially upward displacement of upper die shoe 25 upon eachupward portion of the stroke of ram 11. Each stripper guide bushing 40comprises an open ended, cylindrical tube 48 having an internalpassageway 50, an annular shoulder 52 that projects radially outwardlyfrom a top end 54, and includes a bottom end 55. Internal passageway 50of each stripper guide bushing 40 is defined by the hardened internalsurface of cylindrical tube 48, and is sized to slidingly accept aninternal anti-friction bearing assembly 42 and a guide post 30.

[0029] Each internal anti-friction bearing assembly 42 includes aplurality of circularly and longitudinally spaced ball bearings 56 thatare each confined in a bearing cage 57. Each bearing cage 57 ispreferably cylindrical, and is sized so as to longitudinally enclose andencircle a guide post 30 with appropriate space between guide post 30and bearing cage 57 to avoid contact between them, but to allow for aprestressed loading of ball bearings 56 against the outer surface ofguide post 30. The outer surface of each guide post 30 is hardened,ground, and polished to permit relative longitudinal movement betweenball bearings 56, bearing cage 57, and guide post 30 with good controlso as to prevent relative rotational movement between them. Theforegoing assembly is very often lubricated with an appropriatelyselected oil or other lubricant of the type that is well known in theart.

[0030] Each external anti-friction bearing assembly 44 also includes aplurality of circularly and longitudinally spaced ball bearings 56 thatare each confined in a bearing cage 60. Bearing cage 60 is alsocylindrical, and each is sized so as to (i) longitudinally enclose andencircle a stripper guide bushing 40, and (ii) be received withininternal passageway 32 of lower die shoe guide bushing 31 withappropriate space between lower die shoe guide bushing 31, stripperguide bushing 40 and bearing cage 60 to avoid contact between them. Theouter and inner surfaces of each stripper guide bushing 40 are oftenhardened, ground, and polished to permit relative, self-aligninglongitudinal movement between ball bearings 56 of both internalanti-friction bearing assembly 42 and external anti-friction bearingassembly 44 with good control so as to prevent relative rotationalmovement between them. The foregoing assembly is also very oftenlubricated with an appropriately selected oil or other lubricant wellknown in the art.

[0031] The present invention is assembled to die set 2 in the followingmanner. Stripper-plate 35 is first arranged with a stripper guidebushing 40 press-fit within each peripheral through-bore 37. In thisarrangement, each annular shoulder 52 engages an upper surface ofstripper-plate 35 adjacent to the entrance to a through-bore 37 so as toseat stripper guide bushing 40 within through-bore 37. Internalanti-friction bearing assemblies 42 are then preloadingly press-fitwithin internal passageways 50 of each stripper guide bushing 40. The“prestressing” or “preloading” of internal anti-friction bearingassemblies, i.e., preloading bearings 56 against the internal surface ofstripper guide bushing 40, provides a mechanical coupling of thesestructures, which in turn, allows for a mechanical and structuralcoupling of guide posts 30 and lower die shoe guide bushings 31 tostripper-plate 35. Thus, the internal and external bearing assemblies42,44, provide both anti-frictional movement between guide posts 30,stripper guide bushing 35, and lower die shoe guide bushings 31, and astructural coupling of these structures which effects a highly accurateguidance of these moving parts.

[0032] With stripper guide bushings 40 and internal anti-frictionbearing assemblies 42 assembled to stripper-plate 35, it is thenpositioned between upper die shoe 25 and lower die shoe 26 such thatguide posts 30, stripper guide bushings 40, and lower die shoe guidebushings 31 are arranged in confronting coaxial relation to one another.Coil springs 46 are positioned within recesses 33 at bottom free end 34of each guide post 30. Of course, other arrangements of springs may beutilized to aid in the upward return of stripper-plate 35 withoutdeparting from the present invention. Once in this position, upper dieshoe 25 is moved towards stripper-plate 35 and lower die shoe 26 suchthat guide posts 30 enter internal passageway 50 of each stripper guidebushing 40. It will be understood that internal anti-friction bearingassembly 42 provides smooth relative longitudinal movement between upperdie shoe 25 and stripper guide bushing 40. At the same time,stripper-plate 35 is moved toward lower die shoe 26 so that eachstripper guide bushing 40 enters a lower die guide bushing 31. Eachreturn spring 46 is employed to automatically return die set 2 to anopen position after each downward stroke of ram 11. Here again, externalanti-friction bearing assembly 44 provides for smooth relativelongitudinal movement between each stripper guide bushing 40 and eachlower die guide bushing 31 thereby providing accurate guidance thatallows for a non-fixed engagement between end 21 of ram 11 and upper dieshoe 25.

[0033] In operation, the increased rigidity of alignment provided bystripper-plate alignment system 5 disassociates die set 2 from theover-powering alignment system of press ram 11. In other words, thecombination of internal anti-friction bearing assembly 42, externalanti-friction bearing assembly 44, stripper-plate guide bushings 40 andlower die shoe guide bushings 31 provide an essentially independentguidance system for die set 2 that is not coupled to the guidescontrolling the reciprocating movement of ram 11. In this way, internaland external anti-friction bearing assemblies 42,44 in combination withstripper-plate guide bushings 40 and lower die shoe guide bushings 31alleviate effects from press ram misalignment. As a result of thisimproved arrangement, upper die shoe 25 does not require clamping orbolting t press ram 11, such that bulbous protrusion 24 is freelyreceived within complementary recess 22, i.e., the bulbous protrusion isnot fastened to upper die shoe 25, during operation of the system. Thisarrangement dramatically simplifies and reduces the time required toassemble die set 2 within press 8. In addition, die set 2 may besegmented into upper die shoe and stripper sections with each segmenthaving its own stripper-plate. This enables critical stations in die set2 to operate independently, so that scrap metal produced through thestamping operation does not effect other die stations (FIGS. 9-12).Either a single lower die shoe 26 a may be used (FIG. 12) or a pair oflower die shoes 26 may be mounted upon a locator plate 60 (FIG. 9).

[0034] It is to be understood that the present invention is by no meanslimited only to the particular constructions herein disclosed and shownin the drawings, but also comprises any modifications or equivalentswithin the scope of the claims.

What is claimed is:
 1. A metal stamping system comprising: a pressincluding a ram having a bulbous protrusion projecting outwardly from anend; an upper die shoe including (i) a recess formed in a top surface,said recess being complementary to said bulbous protrusion, and (ii) aplurality of guide posts arranged in a pattern and projecting outwardlyfrom a bottom surface, wherein said bulbous protrusion is receivedwithin said complementary recess; a lower die shoe positioned inconfronting relation to said surface and including a first plurality ofopen ended tubular guide bushings each having a first anti-frictionbearing assembly positioned within a central passageway, and eachlocated so as to receive a corresponding one of said guide posts; and astripper-plate positioned between said upper die shoe and said lower dieshoe, including a second plurality of open-ended tubular guide bushingseach having an outer surface and an inner surface and each projectingoutwardly toward said lower die shoe in a pattern corresponding to saidpattern of guide posts such that each of said first anti-frictionbearing assemblies slidingly engages an outer surface of a correspondingone of said second open ended guide bushing wherein each of said secondplurality of open-ended guide bushings includes a second anti-frictionbearing assembly positioned on said inner surface so as to engage acorresponding one of said guide posts; and spring means for separatingsaid upper shoe from said lower shoe after each downward stroke of saidram.
 2. A metal stamping system according to claim 1 wherein each ofsaid open-ended tubular guide bushings includes an annular shoulder thatprojects radially outwardly from a top end.
 3. A metal stamping systemaccording to claim 1 wherein each of said open-ended tubular guidebushings comprises an internal passageway defined by a hardened surfaceand sized to slidingly accept one of said first anti-friction bearingassemblies.
 4. A metal stamping system according to claim 3 wherein eachof said first anti-friction bearing assemblies includes a plurality ofcircularly and longitudinally spaced ball bearings that are eachconfined in a bearing cage, wherein said ball bearings are preloadedagainst said hardened surface.
 5. A metal stamping system according toclaim 3 wherein each of said first anti-fiction bearing assembliescomprises an open ended tubular cylinder.
 6. A metal stamping systemaccording to claim wherein each of said second anti-friction bearingassemblies includes a plurality of circularly and longitudinally spacedball bearings that are each confined in a bearing cage, wherein saidball bearings are preloaded against a surface of one of said open-endedtubular guide bushings.
 7. A metal stamping system according to claim 6wherein each of said second anti-friction bearing assemblies include abearing cage that is cylindrical.
 8. A metal stamping system accordingto claim 1 wherein said bulbous protrusion projects outwardly from anintermediate plate positioned on an end of said ram.
 9. A metal stampingsystem according to claim 1 comprising a pair of upper die shoes, a pairof lower die shoes, and a pair of stripper-plates positioned betweensaid upper die shoes and said lower die shoes, wherein said pair oflower die shoes is mounted upon an intermediate plate positioned upon abolster.
 10. A die set to be reciprocatingly driven in a stamping presscomprising: an upper die shoe including (i) a recess formed in a topsurface, said recess being complementary to a bulbous protrusion locatedon a ram portion of said press, and (ii) a plurality of guide postsarranged in a pattern and projecting outwardly from a bottom surface,wherein said bulbous protrusion is received within said complementaryrecess; a lower die shoe positioned in confronting relation to saidsurface and including a first plurality of open ended tubular guidebushings each having a first anti-friction bearing assembly positionedwithin a central passageway, and each located so as to receive acorresponding one of said guide posts; and a stripper-plate positionedbetween said upper die shoe and said lower die shoe, including a secondplurality of open-ended tubular guide bushings each having an outersurface and an inner surface and each projecting outwardly toward saidlower die shoe in a pattern corresponding to said pattern of guide postssuch that each of said first anti-friction bearing assemblies slidinglyengages an outer surface of a corresponding one of said second openended guide bushing, wherein each of said second plurality of open-endedguide bushings includes a second anti-friction bearing assemblypositioned on said inner surface so as to engage a corresponding one ofsaid guide posts.
 11. A die set according to claim 10 wherein said upperdie shoe includes at least two of said guide posts that are eachreceived within one of said first open ended tubular guide bushings. 12.A die set according to claim 10 wherein said upper die shoe includes sixguide posts wherein each are received within one of said first openended tubular guide bushings.
 13. A die set according to claim 10wherein each guide post includes a recess defined at a free end, havinga spring mounted therein for separating said upper shoe from said lowershoe after each downward stroke of said ram.
 14. A die set according toclaim 10 wherein said stripper-plate includes a pattern of peripheralthrough-bores arranged in corresponding relation to the positions ofsaid guide posts and said first plurality of open ended tubular guidebushings.
 15. A die set according to claim 10 wherein each of saidsecond plurality of open-ended tubular guide bushings includes aninternal passageway and an annular shoulder that projects radiallyoutwardly from a top end.
 16. A die set according to claim 15 whereineach of said internal passageways is defined by a hardened surface, andis sized to slidingly receive a first anti-friction bearing assembly andone of said guide posts.
 17. A die set according to claim 16 whereineach of said first anti-friction bearing assemblies includes a pluralityof circularly and longitudinally spaced ball bearings that are eachconfined in a bearing cage, wherein said ball bearings are preloadedagainst a said hardened surface.
 18. A die set-according to claim 17wherein said bearing cage is cylindrical, and sized so as tolongitudinally enclose and encircle one of said guide posts.
 19. A dieset according to claim 17 wherein each of said first anti-frictionbearing assemblies is located between said guide post and bearing cageso as to allow for a prestressed loading of said ball bearings againstan outer surface of said guide post.
 20. A die set according to claim 10wherein each of said second anti-friction bearing assemblies includes aplurality of circularly and longitudinally spaced ball bearings that areeach confined in a bearing cage.
 21. A die set according to claim 20wherein each of said bearing cages is cylindrical, and each is sized soas to (i) longitudinally enclose and encircle one of said secondplurality of open-ended tubular guide bushings, and (ii) be receivedwithin one of said first plurality of open ended tubular guide bushings.22. A die set comprising: two upper die shoes positioned adjacent to oneanother, and each including a plurality of guide posts arranged in apattern and projecting outwardly from a surface; two lower die shoespositioned adjacent to one another, and each positioned in confrontingrelation to a respective one of said surfaces, and each including afirst plurality of open ended tubular guide bushings each having a firstanti-friction bearing assembly positioned within a central passageway,and each located so as to receive a corresponding one of said guideposts; and two stripper-plates, one positioned between each pair of saidupper die shoes and said lower die shoes, and each including a secondplurality of open-ended tubular guide bushings each having an Outersurface and an inner surface and each projecting outwardly toward saidlower die shoe in a pattern corresponding to said pattern of guide postssuch that each of said first anti-friction bearing assemblies slidinglyengages an outer surface of a corresponding one of said second openended guide bushing, wherein each of said second plurality of open-endedguide bushings includes a second anti-friction bearing assemblypositioned on said inner surface so as to engage a corresponding one ofsaid guide posts.